1. Field of the Invention
The present invention relates generally to mobile grain harvesting equipment and, more particularly, to combine harvesters and the like in which means for improving the efficiency of the grain separation or harvesting process is provided.
2. Description of the Prior Art
As mobile combines are harvesting in the field, the grain is threshed and separated from the straw and stored in a storage bin within the combine for later delivery to another vehicle for transport from the field. This is the most economical method for harvesting grain. In general, the harvesting process of all combines is alike, that is, the material harvested enters the combine through a header portion and is elevated through the elevator housing into the threshing and separating units within the combine. The threshing and separating units receive the unthreshed crop material and generally separate the grain from the straw by means of a rubbing or beating motion. The grain and other unthreshed crop material separated from the straw falls from the threshing and separating units onto the grain handling and cleaning means while the straw is discharged from the rear of the threshing and separating units onto a beater element which expels the threshed straw through an opening in the hood of the combine.
The grain handling and cleaning means includes means to separate the light straw material or chaff from the grain and means to segregate the unthreshed material (known in the art as tailings) from the grain in order to collect the clean grain in a grain bin or tank located at the top of the combine. The grain handling and cleaning means is generally conventional and comprises oscillating grain pan and sieves and a fan for the separation process. The grain pan, disposed beneath the threshing and separating units, receives the threshed material therefrom and discharges the threshed material to oscillating sieves disposed rearwardly and below the grain pan. That is, the vibration or oscillation of the grain pan causes the grain and threshed material to move rearwardly to be discharged onto the sieves below and thus subjected to the air flow from the grain handling and cleaning fan. The fan, moreover, blows a sufficient volume of air through the apertures provided in the sieves to aerodynamically separate the grain from the chaff. Accordingly, the chaff and other small trash material are suspended in the airstream and are discharged through a rear opening in the combine while the grain drops to the sieves below. The first sieve or chaffer sieve is provided with means for adjusting the apertures such that the grain received thereon may fall therethrough while the larger trash material is shaken rearwardly for discharge out of the combine. In addition, the second or clean grain sieve disposed beneath the first or chaffer sieve includes adjustable apertures such that only the grain drops therethrough to a guide where it may be collected for elevation to the grain bin. Any larger material (generally known in the art as tailings) discharged onto the lower second sieve is discharged rearwardly and collected within the combine to be elevated and discharged into the feed section of the threshing and separating units for reprocessing of the grain attached thereto. Thus, an excellent separation or cleaning of the grain is obtained along with a separate and rapid discharge of straw, trash and chaff material from the combine.
In certain operating conditions, however, perhaps more often with new high capacity combines wherein a large amount of short straw is produced by the threshing operation and in muddy conditions whereby the mud and straw combination form a coagulated mass, the short straw or coagulated straw-mud mass often overloads the cleaning and handling system. Furthermore, if the harvesting operation is being attempted at too great a load for the cleaning means to handle, the threshed material, including the chaff and straw, overloads the cleaning and handling system. When the sieves become overloaded with chaff and trash straw material or the coagulated straw-mud mass, separation of the grain is not performed and a short straw and chaff material mat forms on the sieves further reducing the separation process. In addition, as the mat is moved rearwardly and discharged from the combine, some of the grain entrained therein is also discharged or lost thereby reducing the economic efficiency of the machine and from a practical viewpoint reducing the over-all yield of the harvest.
It has been noted that during the harvesting operation, a localized straw mat buildup on the sieves effectively causes a localized blockage of the air flow through the sieves reducing the aerodynamic separation produced by the fan. Further, as the flow of air through the sieves is blocked, additional straw and chaff material collapse from the airstream onto the straw mat on the sieve forming a tighter and larger mat which progressively grows along the sieve reducing grain separation and increasing grain loss through the rear of the combine. As the blockage of the sieve increases, the increasing incoming material causes the "collapsed area", that is, the area through the sieves in which there is no air flow, to enlarge. In addition, the tailings returns increase dramatically adding more material to the incoming flow. When the straw mat fills the sieve blocking the front part thereof, pure aerodynamic separation fails and the overload is complete. In this stage, the grain is captured in the collapsed mat and rides over the sieve and is discharged onto the ground.
Accordingly, there is a need to provide means for detecting the overload buildup or a localized blockage of the sieves and to indicate this condition to the operator of the combine.